Reporter: When ken Brennan first floated his theory of the crime, that the woman had been attacked by this large man, and dragged out of the airport regency in his suitcase, detective Alan Foote thought it was a bad joke. Are you thinking that maybe he's a little out there? Sometimes we are all out there, but it's a lead. It's not on my priority, because I'm not looking for a black male. I am putting this lead off to the side, while I pursue the leads that I have. Reporter: Even Brennan's employers were skeptical. This is a pretty bizarre theory. How does this go over with the hotel? Well, it didn't really go over with the hotel too much either. In fact, one of the owners said, what the hell kind of an investigator are you? He goes, you're telling me it's this big black guy, everybody else says, and she says it's two white hispanic, you know, where's this coming from? You know? What kind of investigator are you? And they all started laughing inside the room. And that's what really pissed me off. And I said, hell or high water, I'm going to find out. I'm going to prove to these people that I'm right. I know I'm right. I can feel it. I knew this was the guy. And I was going to catch this guy. Reporter: There's some debate among Brennan's clients, the airport regency hotel and its insurer, about whether to continue the investigation and find the attacker, or just settle the lawsuit with inn and walk away. But the hotel's vice president, Jose Vazquez, keeps Brennan in the game. There was no way that we quit that moment. We wanted to go up to the end. So it was because of his little bit of arm-twisting, that we're able to carry on with the investigation. Reporter: Now you're focused on this big tall black guy with a bag that you've seen on camera. The case is pretty cold at this point, he's long gone. How do you even begin to try to find this guy? You know, I didn't know if he was somebody that was staying at the hotel, that was a visitor that was just visiting, you know, one of the other people from the hotel. Or if it's a guy that just walked off the street. We didn't know, so, that was the next part of the investigation. Reporter: The hotel photo copies the I.D.S of registered guests, but as you can see, the facial images are unrecognizable and thus useless. So, you go back to the tape. I go back to the tape. Reporter: And what do you find? I was looking to see if he had any interaction with any of the other people in the hotel. And he does. He ends up interacting with another black fellow. Reporter: And take a look at this -- the second man is often seen wearing a lanyard around his neck, with what looks like a name tag. I'm trying to find out why he's wearing this name tag. Reporter: The problem? It's impossible to make out the name with the naked eye. So Brennan calls up the people who own the most powerful telescopes in the world -- nasa. I say, listen, you know, I know you guys look at, you know, digital photography from, you know, light years away, you know, maybe you could help me out this case that I'm working. Reporter: But for this mission, not even nasa had the right stuff. So, they couldn't do it? No. So, they informed me, listen, you know, we tried, but we're not able to get that for you. So, I said, okay, fine. Let's go back to the tape. Reporter: Fortunately, the next clue is spelled out in bold letters. Later on in the video, when he's out by the hallway, you can clearly see that this says Mercury. But it's -- Reporter: What's Mercury? That was the problem, I didn't know. Reporter: Mercury. Is it the car? The planet? The element? There's no way to tell. Until, in another critical frame of video, Brennan notices another word written on the back of that same shirt. You can clearly make out a "V" and an "O," but it was difficult to make out what was in the middle. And for whatever reason, I don't know, I think that says verado. What the hell's a verado? I don't know, let's find out. So then I went online and did a search. And I got a hit. And it showed that Mercury marine made a brand new outboard engine, by the name of verado. engine, I said, these guys are working at the boat show. Hi! Reporter: In fact, the Miami boat show was held the same week of the crime. And, as usual, Mercury was the major exhibitor. For a second, Brennan feels like he's on the verge of closing the case, assuming the suspect works with the guy in the t-shirt, and they both work for Mercury. It's just a matter of getting someone there to identify him. Mercury marina is actually, the parent company is a company by the name of Brunswick. I end up contacting Brunswick, speaking to the head of security, and I said, listen, did you have any employees that stayed at the airport regency hotel? He said, no, we doesn't. Reporter: So, it's a dead end? So, it's a little bit of a set back. Reporter: So now he must find yet another needle in what's becoming a long row of haystacks. I said, well, trust me, one of the guys there is walking around with one of those Mercury verado shirts, somebody was giving them out. So, he goes, okay, let me get back to you. I said, okay, fine. Couple days later he calls me back, he says, far as we can tell, the only people that received any of the shirts, the verado shirts, were employees that worked at the food court. Reporter: So, another connection. So there's another connection. I said, well, let's find out who's the caterer for the Miami boat show. So, it ends up becoming a company called center plate. Reporter: Another lead, another headache. Center plate tells Brennan it runs concessions at events across the country, and brings in people from all over. It reimburses workers for housing, but doesn't keep track of where they stay. The company is cooperative, but just can't say if any of its people slept at the airport regency. For Brennan, another possible dead end. I've come a long way, and I said, I'm not going to give up on this guy yet. I said, listen, he's really distinctive. The guy's about 6'4", he's a black fellow and he wears glasses, you know, big thick glasses. So, I said, does anybody remember working with a guy that matches that description? Sure enough, about a week or so later, call him again, said, you know, gotten anywhere? He says, listen, he says, nobody knows the guy's name, but one of the people that remembered seeing this fellow working there remembers something about him being hired out of Louisiana. He believes that's where he's from. Reporter: So, now you've gone from Miami to Louisiana. Now I'm over in Louisiana. Reporter: Brennan's man hunt takes a big turn into the big easy. There was no doubt in my mind that if he was on your trail --

This transcript has been automatically generated and may not be 100% accurate.

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{"id":24823383,"title":"Hot on the Trail of Woman's Hotel Attack","duration":"6:53","description":"Act 5: After further investigation, Brennan attempts to identify the man last seen with Inna.","url":"/2020/video/hot-trail-womans-hotel-attack-24823383","section":"2020","mediaType":"Default"}